In knitting operations, especially when yarns of natural fibers, such as cotton, which have a marked tendency to produce lint or fluff, are used, the danger exists that the fluff will stick in the area of the longitudinal slot over the course of time, thereby impeding the freedom of movement of the closing element and preventing the proper operation of the compound needle.
For this reason, in a known compound needle (see German Democratic Republic Pat. No. 93 971, to which British No. 1,347,154 corresponds), a lengthwise opening or slit extending parallel to the longitudinal axis of the slot is located in the bottom surface of the longitudinal slot, so that fluff entering the longitudinal slot can escape through this opening, or slit, thereby preventing jamming of the closing element caused by an accumulation of lint or fluff in the slot. The closing element, which executes a reciprocating movement relative to the needle shank, here performs a cleaning function; that is, in its longitudinal sliding movement it repeatedly carries any fluff located in the slot into the area of the recess or slit and thereby removes it from the longitudinal slot. In order to assure proper guidance of the closing element in the longitudinal slot or groove and to prevent the closing element from being lifted away from the bottom of the longitudinal slot as a result of the force exerted upon it by the yarn, two cross pins are inserted into the side portions of the needle shank defining the longitudinal slot, ahead and behind the opening or slit; these pins extend through associated slots in the closing element. However, since the longitudinal slot or groove is open at the top over its entire length, the lateral stability of this needle is limited, particularly in the area of the opening or slit. If the needle hook is pulled to the side, for instance by lateral forces exerted as the goods are dropped, the danger therefore exists that the closing element will jam in the slot, or in moving toward the needle hook will slide past the hook, with the result that the newly formed loop will not be cast off over the end of the closing element and the needle hook but will become caught in the open needle hook instead, causing flaws in the goods.
Other compound needles, on the other hand, have great stability; such needles have the longitudinal slot or groove closed by elongated guidance elements, acting as stop parts for the butt of the closing element and attached to the edges of the longitudinal groove or slot in the interior of the needle shank by welding, riveting or the like (German Pat. No. 27 05 605, to which U.S. Pat. No. 4,109,490 corresponds). The same is true of still another compound needle (German Pat. No. 1 635 847), in which the needle shank is formed, over a portion of its length, as a tubular section encompassing the compound slider element. In these compound needles, no opening for removing fluff was provided, for the sake of needle stability. The danger that fluff or lint could stick in the vicinity of the closed longitudinal groove over the course of time when working with cotton yarn, for instance, must simply be taken into account with these needles.
Finally, still other compound needles are known (from Swiss Pat. No. 215 641) in which the longitudinal slot or groove disposed in the needle shank is open toward the back of the shank over the entire length of the slit, as far as the area of the cheek taper in the immediate vicinity of the needle hook. On the side remote from the back of the shank, there is a groove-like opening, permitting the passage therethrough of the closing element, only in the area of the needle cheek. In these compound needles, the shank is laterally unstable precisely in the vicinity of the hook, because of the groove-like opening, and thus these needles can withstand only relatively slight lateral forces.